Frame elements for containing monoliths

ABSTRACT

An element frame for holding monoliths containing catalysts in the flow of exhaust gases from a combustion source, the element frame comprising two pairs of opposing walls, wherein the walls form a rectangular or square shape, an interior formed by the walls, an inlet end, an outlet end, at least one locking element, at least one mat and at least one monolith comprising an inlet, an outlet, four sides and at least one catalyst effective in reducing the concentration of one or more gases in the exhaust gas, wherein the at least one mat and the at least one monolith being positioned in the interior of the element frame so that there is at least one mat between the monolith and each adjacent wall, each locking element extending across the inlet end or outlet end of the element frame and being connected to two opposite sides of the element frame.

FIELD OF THE INVENTION

The invention relates to an improved element frame that holds monolithscontaining catalysts within the frame, where the element frame with thecatalyst is configured to be placed in the flow of exhaust gas from anengine.

BACKGROUND OF THE INVENTION

The invention relates to element frames used in catalyst modules fortreating exhaust gases from a stationary combustion source having anexhaust system passing exhaust gases through a support structurecontaining one or more monoliths, each containing one or more catalysts.A stationary combustion system can be any system that combusts ahydrocarbon-based fuel that is not used in an on-road operated car,truck or aircraft. They can be, for example, coal-fired systems,oil-fired (petroleum) systems or gas turbines. Stationary combustionsystems can also be used in marine applications, where combustionsystems such as diesel engines, as used for large container or cruiseships. Stationary combustion systems are usually operated continuouslyunder a constant, stationary load while mobile combustion systems areusually operated under varying loads.

Hydrocarbon combustion in these systems, and in engines used in mobileapplications, generates exhaust gas that must be treated to removepollutants like nitrogen oxides (NOx), carbon monoxide (CO) orhydrocarbons (HC) that are formed. NOx is known to cause a number ofhealth issues for humans and animals as well as causing a number ofdetrimental environmental effects including the formation of smog andacid rain. CO is toxic to humans and animals and HC can cause adversehealth effects. To mitigate both the human and environmental impact fromthese pollutants, especially NO_(x), in exhaust gas, it is desirable toeliminate these undesirable components, preferably by a process thatdoes not generate other noxious or toxic substances.

Stationary combustion systems can be equipped with an emission controlsystem, which is provided with catalyst modules. FIG. 1 is a depictionof a catalyst module known in the art. Catalyst modules are structurescomprising a plurality of element frames, where each element frame cancontain a plurality of monoliths each comprising a catalyst support andone or more catalysts. The catalyst modules are installed in a flue gasduct of the emission control system and the flue gas, which is to bepurified, flows through the monoliths during operation. The flue gasduct can typically have a cross-sectional area of a few square metersand can be in the tens to hundreds of square meters. The dimensions ofthe flue duct can vary widely depending upon many factors, including thesize of the engine, the conditions under which the engine is operated,permissible back pressure, etc. In some cases, the flue gas duct canhave a rectangular cross-section with the width and the height of theduct each being several meters, for example, of 10 m×10 m. The entirecross-sectional area of the flue gas duct is covered by one or morecatalyst modules. The catalyst modules are arranged next to one anotherso that all the flue gas passes through the monoliths, contacts thecatalyst(s) on or in the monoliths and becomes purified. Severalcatalyst modules, for example, two to five, can be placed next to oneanother in rows and columns, often connected in a supporting framework,within the flue gas duct (FIG. 2). The catalyst modules themselvestypically have a rectangular cross-section with an edge length ofseveral meters.

In the direction of flow of the flue gas, catalyst modules frequentlyare located in several planes positioned one behind the other. In someapplications, the catalyst modules can extend for several meters, andeven as much as 10-15 meters in the direction of flow (FIG. 3). For someapplications, such as marine or gas turbines, relatively harsh ambientconditions in terms of mechanical stress can be present for the catalystmodules. For example, on marine vessels, forces several times gravitycan be experienced. In addition, especially for large cross-sections ofcatalyst modules used with gas turbines, mechanical stresses due toearthquakes have to be considered.

Catalyst modules can be constructed using a stacking frame in whichseveral element frame units are inserted, where the element frame unitscontain monoliths comprising one or more catalysts. Flue gas flowsthrough the individual monoliths in the direction of the flue gas flow.The monoliths are also known as honeycomb type catalysts. Thesehoneycomb type catalysts are generally made of a ceramic material andhave a plurality of flow channels through the monolith in the directionof the gas flow. In the installed, operating state, flue gas flowsthrough the flow channels in the monolith where it interacts withcatalyst in the monolith or in a coating on the surface of the monolithand becomes purified.

A typical problem encountered in the use of these treatment systems isthat material placed between the monoliths and the element frameelements to provide a seal and therefore, gas-tightness i.e. no bypassflow around the catalyst, as well as, to act as a cushion againstvibrations, is not able to stay in place during normal use except forwhen the material is specially designed and provided as a special typeof mat that has a relatively high cost. The mat between element frameand a monolith containing one or more catalysts is placed in the elementframe just before the element frame is welded together. In situationswhere there is periodical mechanical stress, which is typical in exhaustsystem conditions where engine pulsation leads to shock and vibrations,the mat can move against the frame and monolith. This movement can causethe destruction of the monolith because of the relatively low mechanicalstability of the system to shock and vibrations.

Current element frames have metal flaps or lips that overlap the inletand/or outlet faces of the monolith so that approximately 15% of thecatalyst cells are not directly exposed to the exhaust flow.

Current element frames also have locking elements in the center of theinlet and outlet face. One of the functions of the locking element is toshield gaps between the monoliths from direct exhaust gas flow. Thelocking element is welded without prestress, which leads to relativelylow mechanical stability against shock and vibrations.

The current designs of element frames do not provide a mechanism toattach the element frames directly to each other. The ability to joinelement frames together can avoid the need for a catalyst module whenonly a small number of element frames are needed.

It would be desirable to have a catalyst module that allows for acost-effective material to be placed between the monoliths and the metalframe of the element frame to provide a seal and to act as a cushionagainst vibrations that can stay in place during normal use and alsoprovide for the largest possible catalyst cross-section to be utilized,all under harsh mechanical stress conditions.

SUMMARY OF THE INVENTION

In a first aspect, the invention relates to an element frame for holdingmonoliths containing catalysts in the flow of exhaust gases from acombustion source, the element frame comprising two pairs of opposingwalls where the walls form a rectangular or square shape, an interiorformed by the walls, an inlet end, an outlet end, at least one lockingelement, at least one mat and at least one monolith comprising an inlet,an outlet, four sides and at least one catalyst effective in reducingthe concentration of one or more gases in the exhaust gas, where the atleast one mat and the at least one monolith is positioned in theinterior of the element frame with at least one mat between the monolithand each adjacent wall, each locking element extending across the inletend or outlet end of the element frame and being connected to twoopposite sides of the element frame.

In a second aspect, the invention relates to a catalyst modulecomprising a plurality of element frames of the first aspect of theinvention.

In another aspect, the invention relates to an exhaust system comprisingan element frame of the first aspect of the invention.

In yet another aspect, the invention relates to an exhaust systemcomprising a catalyst module of the second aspect of the invention.

In still another aspect, the invention relates to a method of making anelement frame of the first aspect of the invention.

In another aspect, the invention relates to a method of making acatalyst module of the second aspect of the invention.

In yet another aspect, the invention relates to a method of treating anexhaust gas, the method comprising passing an exhaust gas throughmonoliths in an element frame of the first aspect of the invention,where the monoliths comprise one or more catalysts effective in reducingthe concentration of one or more gases in the exhaust gas.

In still another aspect, the invention relates to a method of increasingthe amount of catalyst contacted with an exhaust gas, the methodcomprising passing an exhaust gas through a catalyst module of thesecond aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three-dimensional depiction of a catalyst module.

FIG. 2 is a diagram showing the placement of modules across the crosssection of an exhaust duct.

FIG. 3 is a diagram showing an overhead view of the placement of fivegroups of modules placed one after another in the direction of the gasflow within an exhaust duct.

FIG. 4 is a three-dimensional depiction of a frame element.

FIG. 5 is a three-dimensional depiction of a frame element with fourmonoliths in the frame element.

FIG. 6 is a depiction of part of an element frame shown from the inletand/or outlet side showing two pieces each with adjacent wall andcut-outs in the inlet and/or outlet face.

FIG. 7 depicts an end view of a frame element with a locking elementattached.

FIG. 8 depicts a side view of a frame element.

FIG. 9 depicts a cross-sectional view of a frame element with twomonoliths within the cross-section of the frame element.

FIG. 10 depicts a cross sectional view of a protrusion on the frameelement.

FIG. 11 depicts a side view of a frame element comprising fourmonoliths.

FIG. 12 depicts a side view of a frame element comprising six monoliths.

FIG. 13 is a three-dimensional depiction of a frame element with each ofthe sides having an extension for connecting the frame element to otherframe elements.

FIG. 14 is a depiction of two connected locking elements with cut-outs.

FIG. 15 is a three-dimensional depiction of three frame elements withthe sides having extension for connecting the frame element to otherframe elements where the frame elements contain monoliths.

DETAILED DESCRIPTION OF THE INVENTION

As used in this specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly indicates otherwise. Thus, for example, reference to “acatalyst” includes a mixture of two or more catalysts, and the like.

The term “substantially all” means at least 90%, preferably at least95%, preferably at least 97%.

The term “support” means an inert material to which a catalyst is fixed.

The term “element frame” means a structure comprising four walls, eachwall comprising a plurality of protrusions, where the four walls form arectangle or a square, and define an interior of the element frame suchthat a plurality of monoliths, each having at least one mat covering aportion of each side of the monolith. The element frame can also containa locking element on the inlet cross section which is used to shield themat material from direct flow momentum and to act as a tie bar for highmechanical stability. The element frame can be made of steel, where thesteel is any one of a number of different grades.

The term “locking element” means a structure that holds a monolithwithin an element frame. The locking element typically is made of thesame material as the element frame, i.e. steel of any one of a number ofdifferent grades.

The term “cut-out” means a part or section of a frame element or lockingelement that is not present and provides for a reduction in the surfacearea of the frame element or locking element in relation to the flow ofexhaust gas when the frame element or locking element is installed inthe flow of exhaust gas. The cut-out increases the number of cells in amonolith that are directly exposed to the flow of exhaust gas. The term“directly exposed” means that exhaust gas enters cells in the monolithat an opening at the inlet side of the monolith.

A “mat” is to be understood as meaning a combination of mineral, glassor metallic fibers, for example in the form of a woven fabric, a knittedfabric, an irregular layer or the like. The mat may also be referred toas a web, fleece or non-woven material. The fibers used include amaterial which is able to withstand high temperatures and is resistantto corrosion. They can include in particular an iron base material towhich alloying elements are added, with at least one alloying elementbeing selected from nickel (8-11% by weight) or chromium (17-24% byweight) advantageously being present. One example of suitable fiberscomprises 70% by weight of iron, 17% by weight of chromium and 8% byweight of nickel, although standard impurities may of course also bepresent. The mat can be produced by using fibers which are identical ordifferent (for example with regard to the fiber length and fiberdiameter). The fibers used may also comprise a mineral or glass basedmaterial. The mat can be a single piece or can be in the form of stripswhere the strips cover an entire side, or a portion of one or moresides, of a monolith or surround only a portion of the monolith.

The term “catalyst module” means a structure formed by, or containing, aplurality of element frames.

In the first aspect of the invention, an element frame for holdingmonoliths containing catalysts in the flow of exhaust gases from acombustion source, the element frame the element frame comprises twopairs of opposing walls where the walls form a rectangular or squareshape, an interior formed by the walls, an inlet end, an outlet end, atleast one locking element, at least one mat and at least one monolithcomprising an inlet, an outlet, four sides and at least one catalysteffective in reducing the concentration of one or more gases in theexhaust gas, where the at least one mat and the at least one monolith ispositioned in the interior of the element frame with at least one matbetween the monolith and each adjacent wall, each locking elementextending across the inlet end or outlet end of the element frame andbeing connected to two opposite sides of the element frame. At least onewall, preferably each wall, can comprise a plurality of protrusionsextending into the interior of the element frame. The plurality ofprotrusions can be configured to contact a mat and hold the mat againsta monolith comprising one or more catalysts when the monolith is locatedin the interior of the element frame.

FIG. 4 is a three-dimensional depiction of an element frame. The elementframe comprises four walls, and one or more, preferably all of thewalls, can comprise a plurality of protrusions extending into theinterior space formed by the four walls. The frame element can hold aplurality of monoliths within the interior space formed by the fourwalls, as shown in FIGS. 5, 11 and 12. The element frame can hold themonoliths in different configurations, such as 1 by 2, 1 by 3, 3 by 3,etc. The length (depth) of the element frame is based on the length themonoliths and the number of monoliths that may be placed serially withinthe element frame.

When two or more monoliths are present in the interior of the elementframe and at least two monoliths are located adjacent two each other, atleast one mat can be located between monoliths that are adjacent to eachother. Preferably at least a portion of one or more mats is positioned:(a) between each side of a monolith and an adjacent monolith; and (b)between each monolith and an adjacent wall of the element frame.

The element frame can be formed by joining four walls other to form arectangle or a square having an interior. Preferably, the element framecan be formed by joining two pieces, each comprising two walls,together. FIG. 6 shows a view from the inlet end or outlet end of twopieces (A and B), each comprising two walls formed by bending a singlepiece. The walls are not shown as they extend into the figure and arehidden by parts of the element frame at the inlet and/or outlet that arebent toward the interior of the element frame. The parts of the elementframe at the inlet and outlet of the element frame preferably compriseone or more cut-outs that can increase the exposure area of monolithsplaced within the element frame. Cut-outs of the element frame on theinlet and outlet face can reduce the number of cells in a monolith thatare not directly seeing the exhaust flow. Preferably less than 10%, morepreferably less than 8%, even more preferably less than 7%, even morepreferably less than 6%, most preferably less than 5% of the catalystcells are not directly exposed the exhaust flow. The reduction in thenumber of cells in the monolith that are not directly exposed to the gasflow can lead to lower back pressure, increase exposure of the exhaustgas to catalysts and higher conversion of compounds in the exhaust gasto other more desired compounds.

Pieces comprising the wall can be connected together, preferably bywelding.

FIG. 7 depicts a view of an element frame from an inlet or outlet endwith two locking elements attached. Monoliths with their side wall atleast partially covered by mats are placed within the walls of theelement frame. Each locking element can be connected to each of the foursides by welding. The locking elements shown in FIG. 7 do not havecut-outs. Preferably the locking elements will comprise one or morecut-outs.

FIG. 8 depicts a side view of a frame element where the wall of theframe element has a length that is approximately the same as the lengthof the monolith. The width of the wall of the frame is dependent uponwhether a single monolith or a plurality of monoliths, preferably two orthree, are located adjacent to each other against the wall. When only asingle monolith is located against a wall, the width of the wall isapproximately equivalent to the size of the monolith against the wallplus the thicknesses of two mats. When a plurality of monoliths islocated against a wall, the width of the wall is approximatelyequivalent to sum of the size of the monolith against the wall plus thenumber of monoliths times the thicknesses of two mats. Depending uponhow the walls are put together, allowance may need to be made for thethickness of the walls and manufacturing tolerance of the monoliths.

FIG. 9 depicts a cross-sectional view of the frame element showing thechannels through the monoliths and protrusions in the walls of theelement frame. In this drawing two monoliths are placed next to eachother with their flow channels having the same direction of flow. Thesection of the drawing labeled “Z” is shown enlarged in FIG. 10 to showdetails of the protrusions.

Two or more monoliths can be placed serially within an element frame, asshown in FIGS. 11 and 12. The element frame can comprise a plurality ofmonoliths where two or more monoliths are positioned so that the outletof a first monolith is adjacent to the inlet of a second monolith and aflow of exhaust gas passes sequentially through at least two monoliths.When three or more monoliths are used, exhaust gas exiting the secondmonolith can enter a third monolith. In these configurations one or moremonoliths can be located downstream of one or more monoliths in thedirection of flow of the exhaust gas through the monoliths in theelement frame.

The element frame can comprise a plurality of monoliths where the two ormore monoliths positioned so that the outlet of one monolith is adjacentto the inlet of another monolith contain catalysts having the samefunctionality. The term “having the same functionality” means that thecatalysts adjacent to each other perform the same type of chemicalreactions, such as selective catalytic reduction (SCR), ammoniaoxidation, hydrocarbon oxidation, NOx storage, oxygen storage, etc.

The element frame can comprise a plurality of monoliths where two of thetwo or more monoliths positioned so that the outlet of one monolith isadjacent to the inlet of another monolith contain catalysts havingdifferent functionality. The term “having different functionality” meansthat the catalysts adjacent to each other perform different types ofchemical reactions. Numerous types of configuration are possible. Forexample, a monolith comprising catalysts for selective catalyticreduction (SCR) can be followed by a monolith comprising catalysts forammonia oxidation. A monolith comprising catalysts for hydrocarbonoxidation can be followed by a monolith comprising catalysts forselective catalytic reduction (SCR). A monolith comprising a catalystproviding NOx storage can be followed by a monolith comprising catalystsfor SCR. Other possible combinations of catalysts are known to thoseskilled in the art.

At least one wall of the element frame can comprise an extended section,where the extended section comprises a plurality of openings, where theopenings are configured to allow a fastener for joining the elementframe to another element frame to pass through the opening.

At least two walls of the element frame can comprise an extended sectioncomprising a plurality of openings, where the openings are configured toallow a fastener for joining the element frame to another element frameto pass through the opening.

Each of the four sides of the element frame can comprise an extendedsection comprising a plurality of openings, where the openings areconfigured to allow a fastener for joining the element frame to anotherelement frame to pass through the opening.

Extended sections can be present on the inlet side, the outlet side, orboth the inlet and outlets sides of the frame element. FIG. 13 shows anelement frame where each of the sides (30) contain an extended section(34) comprising a plurality of openings. Two types of openings, holesand slots are shown in FIG. 13. Other shapes, or combinations of shapes,can be used.

Protrusions

One of more walls, preferably each wall, can comprise a plurality ofprotrusions extending into the interior.

The number and size of the protrusions on a wall can vary depending uponseveral factors, including, but not limited to the physical propertiesof the mat, the size of the mat and the number of mats used per wall,and the size of the wall of the element frame. FIG. 7 shows an elementframe with each wall having 25 protrusions in a 5×5 matrix.

The function of the protrusions is to hold the mat between wall andmonolith to suppress destruction of, or damage to, the monolith by shearforces. When a single mat is used to cover all four sides of themonolith, a smaller number of protrusions may be needed that when two ormore mats are used to cover each side of the monolith. If the mat is inthe form of strips where two or more strips are used on a side of amonolith, more protrusions would be needed that when a single mat isused to cover all four sides of the monolith. FIG. 9 depicts a crosssectional view of a protrusion on the frame element, where theprotrusion has a height (h) and a base of width (w). The greater theheight of a protrusion relative to the area of the base of theprotrusion, the more likely that the protrusion can disturb the matduring normal use due to vibrations. However, a protrusion having asmall height relative to the area of the base of the protrusion can beless likely to disturb the mat during normal use, and the relativelylarge base is better able to contact a larger surface area of the mat.The height of the protrusion can be about 1 mm and the protrusion can beabout 6 mm wide. Depending upon the properties of the mat, the thicknessof the wall of the element frame and the material, protrusions havingother height and widths can be used, such as, for example, 2 mm×10 mm,or 1 mm×10 mm. A mat can be cut into large strips having a widthapproximately the same as the depth of the monolith. The mat can then bewrapped around the monolith, and then the monolith covered with the matcan be placed into the element frame. The mat can also be present as twoof more strips, where the combined widths of the strips are less than orequal to the depth of the monolith. When two strips are used and thecombined widths of the strips are less than the depth of the monolith,it is preferable that the strips are positioned off-center. The elementframe is compressed and then the sides are welded together and a lockingelement is attached by welding to the four walls of the element frame onthe inlet end and the outlet end.

The element frame according to the invention has an improved openfrontal area for catalyst use of the exhaust gas while providingimproved mechanical stability against shock and vibrations.

Monolith

The term “monolith”, also known as a “honeycomb” type catalyst means acarrier having a plurality of fine, parallel gas flow passages extendingfrom an inlet to an outlet face of the monolith, such that passages areopen to fluid flow. A monolith can have a rectangular, preferablysquare, cross-sectional and inflow surface. The face of the monolithscan be of any dimensions, preferably between 10 cm to 30 cm, inclusive.The length of monolith in the direction of flow typically ranges from 15cm to 150 cm, although other lengths can be used. The width of theelement frame in the direction of exhaust gas flow is approximately thelength of the monolith.

A monolith has an inlet, an outlet, four sides and a plurality of flowpassages (or “cells”). Monoliths can contain up to about 700 or moreflow passages per square inch of cross section, although far fewer maybe used. For example, for stationary applications the carrier typicallymay have from about 9 to 600, more usually from about 35 to 300, cellsper square inch (“cpsi”). The passages, which are essentially straightpaths from their fluid inlet to their fluid outlet, are defined by wallsonto which one or more catalysts effective in treating exhaust gases arecoated as a “washcoat” so that the gases flowing through the passagescontact the catalytic material.

One of ordinary skill in the art is familiar with the use and selectionof one of more catalysts to reduce nitrogen oxides, carbon monoxides,hydrocarbons, ammonia slip and other pollutants to form nitrogen, waterand carbon dioxide, which are relatively harmless compounds. Themonolith can comprise one or more of an SCR catalyst, an ammoniaoxidation catalyst, a hydrocarbon oxidation catalyst, a NOx storagecatalyst, an oxygen storage catalyst, etc. The monolith can be a filter,such as a ceramic filter. Other types of catalyst can be present. Theflow passages of the monolithic substrate are thin-walled channels whichcan be of any suitable cross-sectional shape such as trapezoidal,rectangular, square, triangular, sinusoidal, hexagonal, oval, circular,etc. The invention is not limited to a particular substrate type,material, or geometry. The monolith is generally an extruded material,preferably a ceramic substrate.

Ceramic substrates may be made of any suitable refractory material, suchas cordierite, cordierite-α alumina, α-alumina, silicon carbide, siliconnitride, zirconia, mullite, spodumene, alumina-silica magnesia,zirconium silicate, sillimanite, magnesium silicates, zircon, petalite,aluminosilicates and mixtures thereof. The ceramic substrate can havecatalytic activity itself. In some cases, no additional catalystmaterial is placed on ceramic substrates having catalytic activity.

Mats

One or more mats can form a seal restricting exhaust gas movement aroundthe monolith. The mats can prevent direct physical contact between themonolith and the element frame and provide damping against shock andvibrations brought onto the element frame from external forces. Matsthat can be used in this invention are known in the art.

A single mat can cover substantially all of the four sides of amonolith. At least a majority of each of the four sides of a monolithcan be covered by a mat. A single mat can cover substantially all of thefour sides of a monolith. One or more pieces of mat can surround all, oralmost all, of the monolith. The mat can be in the form of strips andthe strips can surround only a portion of the monolith.

At least a majority of the area of at least one side of a monolith canbe covered by one or more mats.

At least a majority of the area of each of at least two sides of amonolith can be covered by one or more mats.

At least a majority of the area of each of the four sides of a monolithcan be covered by one or more mats.

The thickness of the mat can be chosen such that the mat fills a gapbetween the monolith and the frame element and provides cushioning thatallows the monolith to withstand a surface pressure of at leastapproximately 100, preferable approximately 150, more preferablyapproximately 200 Newtons/mm² of surface pressure when the element frameis pressed together during assembly.

The thickness of one or more mats that are used with a monolith can bedetermined based upon the size of the monolith onto which the mat is incontact. Monoliths are commercially available in a variety of sizes,with the tolerance of each size monolith being dependent upon themanufacturer. A monolith having a 150×150 mm cross-section can have atolerance of ±3 mm. By having mats with different thicknesses, monolithhaving an actual cross-section of 149×149 mm would use a mat that isthicker than that used for a monolith having an actual cross-section of153×153 mm. The mat used on the monolith having an actual cross-sectionof 153×153 mm would be thinner than the mat used on a monolith having anactual cross-section of 150×150 mm.

When the monolith has a nomimal width N and an actual width A, thethickness of a mat used with a monolith having an actual width A equalto the nominal width N is B, and the desired thickness of a mat usedwith a monolith having an actual width C is:

B+(A−C) when C<A;   a)

B when C=A; and   b)

B−(C−A) when C>A,   c)

where the actual thickness of the mat used with a monolith having anactual width C is the closest thickness of commercially available mat ofthe material of width B.

Two mats can be used to obtain the desired thickness.

Locking Element

The element frame comprises one or more locking elements where eachlocking element extends across the inlet end and/or outlet end of theelement frame and is connected to opposite walls of the element frame.The locking elements hold the monoliths within the element frame andpreclude the movement of opposite walls of the element frame. FIGS. 5and 13 each show an element frame containing four monoliths in a 2 by 2configuration with two locking elements, where each locking element isover the sides of two adjacent monoliths and a gap between themonoliths. In the case of a 1 by 3 monolith element frame, the inletside and the outlet side each side can each comprise two lockingelements, with each of the locking element located over a gap betweentwo adjacent monoliths.

The locking elements preferably contain one or more cut-out. The cutoutprovides for an increase in the number of cells in the monolith that aredirectly exposed to the flow of exhaust gas when the catalyst module isexposed to exhaust gas from an exhaust gas source. When a lockingelement does not comprise cut-outs, a larger number of cells in themonoliths are covered by the locking element and this reduces the numberof cells that come in direct contact with the exhaust gas. The width ofthe cut-out locking element is such that the gap between the monolithsis covered. In determining the width of the cut-out, the productiontolerance of the widths of the monoliths should be considered. Lockingelements located on the element frame on the inlet and outlet face cancontain cut outs so that preferably less than 10%, more preferably lessthan 8%, even more preferably less than 7%, even more preferably lessthan 6%, most preferably less than 5% of the catalyst cells are notdirectly exposed the exhaust flow. This leads to lower back pressure andhigher utilisation of the catalyst monoliths and therefore higherconversion.

When at least one of (a) the walls of an element frame in the inlet andoutlet of the element frame (as shown in FIGS. 6, 7 and 13) and (b) alocking element (as shown in FIGS. 13 and 14), comprise a cut-out, theamount of conversion of at least one of NH₃, NOx, hydrocarbons andcarbon monoxide is greater than that of a comparable element frame nothaving cut-outs.

FIG. 7 depicts a view of an element frame from an inlet or outlet endwith two locking elements attached. Monoliths with their side wall atleast partially covered by mats are placed within the walls of theelement frame. Each locking element can be connected to opposing wallsby welding. The locking element is preferably welded into the elementframe under prestress, which minimizes or prevents bulging of theelement frame. Bulging of the element frame can lead to lower surfacepressure and therefore a higher risk of movement of the monoliths underperiodical mechanical stress like shock and vibrations in typicalexhaust system conditions.

Catalyst Module

In another aspect of the invention, a catalyst module can comprise anelement frame of the first aspect of the invention.

Catalyst modules of the invention can be in one of two groups: having aperipheral frame and without a peripheral frame.

Catalysts modules with a peripheral frame are known in the art, as shownfor example in FIG. 1. Catalysts modules with a peripheral frame canhave two sides 10, a top 11, a bottom 12 and a number of spaces 15formed by horizon partitions 13 and vertical partitions 14. An elementframe 20 of the first aspect of the invention, containing a plurality ofmonoliths comprising one or more catalysts, can be inserted within eachof the spaces 15. Preferably the frame elements comprise one or morelocking elements, as described above.

A catalyst module without a peripheral frame can be formed by combininga plurality of element frames to each other by placing frame elementadjacent to each other and placing element frames on top of other frameelements and connecting frame elements to adjacent frame elements. (SeeFIG. 15) A catalyst module without a peripheral frame is especiallyuseful when only a small number of monoliths are need and the extraweight and complexity in using a catalyst module with a peripheral framecan be avoided.

Preferably, the frame elements are connected to adjacent frame elements.Adjacent frame elements can have a sealing element, such as a mat,located between them. Frame element can be connected to adjacent frameelements by welding, adhesives that can withstand temperatures,vibrations and shocks that the catalyst modules are subject to whenplaced in an exhaust gas stream or mechanical means, such as bolts,nuts, anchors, etc. Preferably, one or more sides of the element framescomprise an extension

The element frames in the catalyst module can be arranged to minimizethe passage of exhaust gas bypass around the element frames when thecatalyst module is installed in an exhaust system.

A catalyst module can comprise a plurality of element frames where atleast one wall of the element frame comprises an extended sectioncomprising a plurality of openings, where the openings are configured toallow a fastener for joining the element frame to another element frameto pass through the opening and each element frame is connected to oneor more elements frames through an extended section on the elementframes.

A catalyst module comprising a plurality of element frames where atleast one wall of the element frame comprises an extended sectioncomprising a plurality of openings, where the openings are configured toallow a fastener for joining the element frame to another element frameto pass through the opening and the element frames are arranged so thatthere is minimal exhaust bypass around the element frames.

A catalyst module can comprise a plurality of element frames where atleast two walls of the element frame comprise an extended sectioncomprising a plurality of openings, where the openings are configured toallow a fastener for joining the element frame to another element frameto pass through the opening and the element frames are arranged so thatthere is minimal exhaust bypass around the element frames

A catalyst module can comprise a plurality of element frames where eachof the four sides of the element frame comprise an extended sectioncomprising a plurality of openings, where the openings are configured toallow a fastener for joining the element frame to another element frameto pass through the opening and the element frames are arranged so thatthere is minimal exhaust bypass around the element frames.

Each of the frame elements in the catalyst module can be connected to anadjacent frame element when the frame elements comprise an extendedsection comprising a plurality of openings, where the openings areconfigured to allow a fastener for joining the element frame to anotherelement frame to pass through the opening.

Each of the frame elements in the catalyst module can be connected toall adjacent frame elements when the frame elements comprise an extendedsection comprising a plurality of openings, where the openings areconfigured to allow a fastener for joining the element frame to anotherelement frame to pass through the opening.

A catalyst module can further comprise a plurality of spaces formed byhorizontal partitions and vertical partitions, where a frame elementcontaining a monolith and one or more mats located between each side ofthe each monolith is present within a space.

The catalyst modules can be fixed directly into the exhaust duct or intoa larger reaction space, called reactor, into the exhaust stream.

An exhaust system can comprise an element frame of the first aspect ofthe invention.

An exhaust system can comprise a catalyst module comprising an elementframe of the first aspect of the invention.

When the monolith in an element frame, either alone or in a catalystmodule, comprises an SCR catalyst, an exhaust system can furthercomprise a means for injecting a reductant fluid, e.g. a hydrocarbon ornitrogenous reductant or a precursor thereof, into exhaust gas upstreamof the .element frame. Preferably the means comprises an injector. Oneof ordinary skill in the art would realize that ammonia or some othertype of reductant is needed when an SCR catalyst is used to convertnitrogen oxides into nitrogen. Such a person would understand how to addthe reactant into the exhaust gas and use the SCR catalyst in thesystem. Such a person would also understand that means for injecting areductant fluid into exhaust gas upstream are well known in the art.

In still another aspect, the invention relates to a method of making anelement frame of the first aspect of the invention. A method of makingan element frame of the first aspect of the invention comprises wrappingeach monolith with a mat, placing the wrapped monolith within theinterior of the element frame before the locking element is connected tothe element frame and connecting the locking elements to the elementframe while the element frame containing the mat wrapped monolith issubject to a compression force. Preferably the element frame iscompressed with a pressure of at least approximately 100 Newtons/mm²,preferably at least approximately 150 Newtons/mm², more preferably atleast approximately 200 Newtons/mm², depending on the nature of the mat.

In another aspect, the invention relates to a method of making acatalyst module comprising a plurality of element frames of the firstaspect of the invention. The method comprises forming an element framecomprising one or more monoliths, one or more mats and one or morelocking elements by wrapping each monolith with a mat, placing thewrapped monolith within the element frame, connecting the one or morelocking elements to the element frame while the element frame containingthe mat wrapped monolith is subject to a compression force and either(a) connecting one or more element frames to each other to form acatalyst module, or (b) inserting the element frame containing the oneor more locking elements into a partition in a frame in a catalystmodule. Preferably the element frame is compressed with a pressure of atleast approximately 100 Newtons/mm², preferably at least approximately150 Newtons/mm², more preferably at least approximately 200 Newtons/mm²,depending upon the nature of the mat. One of ordinary skill in the artwould be familiar with techniques and procedures used to produce acatalyst module having a peripheral frame where the element framesdescribed above can be placed within partitions in the element frame.Such a person would also be familiar with techniques and procedures usedto connect element frames comprising an extension, as described above,to each other using mechanical fasteners.

A method of treating an exhaust gas comprises passing an exhaust gasthrough a monolith within an element frame of the first aspect of theinvention, where the monolith comprises one or more catalysts effectivein reducing the concentration of one or more gases in the exhaust gas.

A method of increasing the amount of catalyst contacted with an exhaustgas comprising passing an exhaust gas through an element frame of thefirst aspect of the invention where the element frame comprises acut-out.

The invention can also be defined according to one or more of thefollowing definitions:

-   1) An element frame for holding monoliths containing catalysts in    the flow of exhaust gases from a combustion source, the element    frame comprising two pairs of opposing walls where the walls form a    rectangular or square shape, an interior formed by the walls, an    inlet end, an outlet end, at least one locking element, at least one    mat and at least one monolith comprising an inlet, an outlet, four    sides and at least one catalyst effective in reducing the    concentration of one or more gases in the exhaust gas, where the at    least one mat and the at least one monolith is positioned in the    interior of the element frame with at least one mat between the    monolith and each adjacent wall, each locking element extending    across the inlet end or outlet end of the element frame and being    connected to two opposite sides of the element frame.-   2) The element frame of 1), wherein two or more monoliths are    present in the interior of the element frame, at least two monoliths    are located adjacent two each other, and at least one mat is located    between monoliths that are adjacent to each other.-   3) The element frame of 1) or 2), wherein at least two locking    elements are located on the inlet end of the element frame and at    least two locking elements are located on the outlet end of the    element frame.-   4) The element frame of any of 1) to 3), where, when the element    frame comprises at least two monoliths, a space is located between    adjacent monoliths and at least one of the locking elements are    located over, and preferably centered on, space between two    monoliths.-   5) The element frame of any of 1) to 4), wherein each locking    element is connected to opposing walls by welding.-   6) The element frame of any of 1) to 5), where the locking element    comprises a cut-out, where the cutout provides for an increase in    the number of cells in the monolith that are directly exposed to the    flow of exhaust gas when the catalyst module is exposed to exhaust    gas from an exhaust gas source.-   7) The element frame of any of 1) to 6), wherein at least one of (a)    the walls of an element frame in the inlet and outlet of the element    frame and (b) a locking element, comprise a cut-out, the amount of    conversion of at least one of NH₃, NO_(x), hydrocarbons and carbon    monoxide is greater than that of a comparable element frame not    having cut-outs.-   8) The element frame of any of 1) to 7), where each wall comprises a    plurality of protrusions extending into the interior.-   9) The element frame of 8), where the plurality of protrusions are    configured to contact a fiber mat and hold the fiber mat against a    monolith comprising one or more catalyst when the monolith is    located in the interior of the element frame.-   10) The element frame of any of 1) to 9), wherein at least one wall    of the element frame comprises an extended section comprising a    plurality of openings, where the openings are configured to allow a    fastener for joining the element frame to another element frame to    pass through the opening.-   11) The element frame of any of 1) to 10), wherein at least two    walls of the element frame comprise an extended section comprising a    plurality of openings, where the openings are configured to allow a    fastener for joining the element frame to another element frame to    pass through the opening.-   12) The element frame of 1) to 11), wherein each of the four sides    of the element frame comprise an extended section comprising a    plurality of openings, where the openings are configured to allow a    fastener for joining the element frame to another element frame to    pass through the opening.-   13) The element frame of any of 1) to 12), where at least a majority    of the area of at least one side of a monolith is covered by one or    more mats.-   14) The element frame of any of 1) to 13), where at least a majority    of the area of each of at least two sides of a monolith is covered    by one or more mats.-   15) The element frame of any of 1) to 14), where at least a majority    of the area of each of the four sides of a monolith is covered by    one or more mats.-   16) The element frame of any of 1) to 15), where the mat is in the    form of strips and the strips surround only a portion of the    monolith.-   17) The element frame of any of 1) to 16), where the thickness of    the mat is chosen such that the mat fills a gap between the monolith    and the frame element and provides cushioning that allows the    monolith to withstand a surface pressure of at least approximately    100, preferable at least approximately 150, more preferably at least    approximately 200 Newtons/mm² of surface pressure when the element    frame is pressed together during assembly.-   18) The element frame of any of 1) to 17), where the monolith has a    nomimal width N and an actual width A, the thickness of a mat used    with a monolith having an actual width A equal to the nominal width    N is B, and the desired thickness of a mat used with a monolith    having an actual width C is:

B+(A−C) when C<A;   a)

B when C=A; and   b)

B−(C−A) when C>A,   c)

where the actual thickness of the mat used with a monolith having anactual width C is the closest thickness of commercially available mat ofthe material of width B.

-   19) The element frame of any of 1) to 18), where one or more mats    form a seal restricting exhaust gas movement around the monolith.-   20) The element frame of any of 1) to 19), where the monolith    comprises an SCR catalyst.-   21) The element frame of any of 1) to 20), where the monolith    comprises an oxidation catalyst.-   22) The element frame of any of 1) to 21), where the monolith is a    filter.-   23) The element frame of any of 1) to 22), wherein the element frame    comprises a plurality of monoliths and two or more monoliths are    positioned so that the outlet of one monolith is adjacent to the    inlet of another monolith and a flow of exhaust gas passes    sequentially through at least two monoliths.-   24) The element frame of 23), where the two or more monoliths    positioned so that the outlet of one monolith is adjacent to the    inlet of another monolith contain catalysts having the same    functionality.-   25) The element frame of 23), where two of the two or more monoliths    positioned so that the outlet of one monolith is adjacent to the    inlet of another monolith contain catalysts having different    functionality.-   26) A catalyst module comprising a plurality of element frames of    any one of 1) to 25).-   27) The catalyst module of 26), where the element frames are    arranged to minimize the passage of exhaust gas bypass around the    element frames when the catalyst module is installed in an exhaust    system.-   28) A catalyst module comprising a plurality of element frames of    one or more of 10), 11), and 12), where each element frame is    connected to one or more elements frames through an extended section    on the element frames.-   29) A catalyst module comprising a plurality of element frames of    one or more of 10), 11), and 12), where the element frames are    arranged so that there is minimal exhaust bypass around the element    frames.-   30) A catalyst module of any one of 26)-29), wherein each of the    frame elements is connected to an adjacent frame element.-   31) A catalyst module of any one of 26)-29), wherein each of the    frame elements is connected to all adjacent frame elements.-   32) A catalyst module of any one of 26)-31), wherein the catalyst    module further comprises a plurality of spaces formed by horizontal    partitions and vertical partitions, where a frame element containing    a monolith and one or more mats located between each side of the    each monolith is present within a space.-   33) An exhaust system comprising an element frame of any one of 1)    to 25).-   34) An exhaust system comprising a catalyst module of any one of 26)    to 32).-   35) An exhaust system of 33) or 34), further comprising a means for    forming NH₃ in the exhaust gas, where the means for forming NH₃ is    located before the element frame or catalyst module.-   36) A method of making an element frame of any one of 1) to 25), the    method comprising wrapping each monolith with a mat, placing the    wrapped monolith within the interior of the element frame before the    locking element is connected to the element frame and connecting the    locking elements to the element frame while the element frame    containing the mat wrapped monolith is subject to a compression    force.-   37) The method of 36), where the element frame is compressed with a    pressure of at least approximately 100 Newtons/mm², preferably at    least approximately 150 Newtons/mm², more preferably at least    approximately 200 Newtons/mm².-   38) A method of making a catalyst module of any one of 26) to 32),    the method comprising forming an element frame comprising one or    more monoliths, one or more mats and one or more locking elements by    wrapping each monolith with a mat, placing the wrapped monolith    within the element frame, connecting the one or more locking    elements to the element frame while the element frame containing the    mat wrapped monolith is subject to a compression force and    either (a) connecting one or more element frames to each other to    form a catalyst module, or (b) inserting the element frame    containing the one or more locking elements into a partition in a    frame in a catalyst module.-   39) The method of 38), where the compression force is at least    approximately 100 Newtons/mm², preferably at least approximately 150    Newtons/mm², more preferably at least approximately 200 Newtons/mm².-   40) A method of treating an exhaust gas, the method comprising    passing an exhaust gas through a monolith within an element frame of    any one of 1) to 25), where the monolith comprises one or more    catalysts effective in reducing the concentration of one or more    gases in the exhaust gas.-   41) A method of increasing the amount of catalyst contacted with an    exhaust gas, the method comprising passing an exhaust gas through an    element frame of one of 6) or 7).

1. An element frame for holding monoliths containing catalysts in theflow of exhaust gases from a combustion source, the element framecomprising two pairs of opposing walls where the walls form arectangular or square shape, an interior formed by the walls, an inletend, an outlet end, at least one locking element, at least one mat andat least one monolith comprising an inlet, an outlet, four sides and atleast one catalyst effective in reducing the concentration of one ormore gases in the exhaust gas, where the at least one mat and the atleast one monolith is positioned in the interior of the element framewith at least one mat between the monolith and each adjacent wall, eachlocking element extending across the inlet end or outlet end of theelement frame and being connected to two opposite sides of the elementframe.
 2. The element frame of claim 1, wherein two or more monolithsare present in the interior of the element frame, at least two monolithsare located adjacent two each other, and at least one mat is locatedbetween monoliths that are adjacent to each other.
 3. The element frameof claim 1, wherein at least two locking elements are located on theinlet end of the element frame and at least two locking elements arelocated on the outlet end of the element frame.
 4. The element frame ofclaim 1, where, when the element frame comprises at least two monoliths,a space is located between adjacent monoliths and at least one of thelocking elements are located over, and preferably centered on, spacebetween two monoliths. 5-7. (canceled)
 8. The element frame of claim 1,where each wall comprises a plurality of protrusions extending into theinterior.
 9. (canceled)
 10. The element frame of claim 1, wherein atleast one wall of the element frame comprises an extended sectioncomprising a plurality of openings, where the openings are configured toallow a fastener for joining the element frame to another element frameto pass through the opening. 11-16. (canceled)
 17. The element frame ofany of claim 1, where the thickness of the mat is chosen such that themat fills a gap between the monolith and the frame element and providescushioning that allows the monolith to withstand a surface pressure ofat least approximately 100, Newtons/mm² of surface pressure when theelement frame is pressed together during assembly.
 18. The element frameof claim 1, where the monolith has a nominal width N and an actual widthA, the thickness of a mat used with a monolith having an actual width Aequal to the nominal width N is B, and the desired thickness of a matused with a monolith having an actual width C is:B+(A−C) when C<A;   a)B when C=A; and   b)B−(C−A) when C>A,   c) where the actual thickness of the mat used with amonolith having an actual width C is the closest thickness ofcommercially available mat of the material of width B.
 19. (canceled)20. The element frame of claim 1, where the monolith comprises an SCRcatalyst or an oxidation catalyst.
 21. (canceled)
 22. The element frameof claim 1, where the monolith is a filter.
 23. The element frame ofclaim 1, wherein the element frame comprises a plurality of monolithsand two or more monoliths are positioned so that the outlet of onemonolith is adjacent to the inlet of another monolith and a flow ofexhaust gas passes sequentially through at least two monoliths.
 24. Theelement frame of claim 23, where the two or more monoliths positioned sothat the outlet of one monolith is adjacent to the inlet of anothermonolith contain catalysts having the same functionality.
 25. Theelement frame of claim 23, where two of the two or more monolithspositioned so that the outlet of one monolith is adjacent to the inletof another monolith contain catalysts having different functionality.26. A catalyst module comprising a plurality of element frames ofclaim
 1. 27. (canceled)
 28. A catalyst module comprising a plurality ofelement frames claim 10, where each element frame is connected to one ormore elements frames through an extended section on the element frames.29. (canceled)
 30. A catalyst module of claim 26, wherein each of theframe elements is connected to an adjacent frame element.
 31. (canceled)32. A catalyst module of claim 26, wherein the catalyst module furthercomprises a plurality of spaces formed by horizontal partitions andvertical partitions, where a frame element containing a monolith and oneor more mats located between each side of each monolith is presentwithin a space.
 33. An exhaust system comprising an element frame ofclaim
 1. 34. An exhaust system comprising a catalyst module of claim 26.35. An exhaust system of claim 33, further comprising a means forforming NH₃ in the exhaust gas, where the means for forming NH₃ islocated before the element frame or catalyst module.
 36. A method ofmaking an element frame of claim 1, the method comprising wrapping eachmonolith with a mat, placing the wrapped monolith within the interior ofthe element frame before the locking element is connected to the elementframe and connecting the locking elements to the element frame while theelement frame containing the mat wrapped monolith is subject to acompression force.
 37. (canceled)
 38. A method of making a catalystmodule of claim 26, the method comprising forming an element framecomprising one or more monoliths, one or more mats and one or morelocking elements by wrapping each monolith with a mat, placing thewrapped monolith within the element frame, connecting the one or morelocking elements to the element frame while the element frame containingthe mat wrapped monolith is subject to a compression force and either(a) connecting one or more element frames to each other to form acatalyst module, or (b) inserting the element frame containing the oneor more locking elements into a partition in a frame in a catalystmodule.
 39. The method of claim 38, where the compression force is atleast approximately 100 Newtons/mm².
 40. A method of treating an exhaustgas, the method comprising passing an exhaust gas through a monolithwithin an element frame of claim 1, where the monolith comprises one ormore catalysts effective in reducing the concentration of one or moregases in the exhaust gas.
 41. (canceled)